LEACHING IN THE PRESENCE OF ABRASIVE

Abstract: The invention relates to a process for leaching copper and/or nickel values from feed solids with a lixiviant containing ammonia and ammonium bisulfite with agitation in the presence of relatively larger abrasive solids and an oxidant, preferably air or oxygen. The solids scrub the surface of the feed solids and aid in the constant exposure of fresh surfaces for increased leaching kinetics as well as overall extractions. The process is particularly useful for solids containing copper sulfides.

Description: LEACHING IN THE PRESENCE OF ABRASIVE FIELD OF THE INVENTION The present invention relates to a process for leaching copper and/or nickel from sources containing copper and/or nickel. Exemplary sources include concentrates, ores, slag, and flue dust. BACKGROUND OF THE INVENTION The art has suggested several methods for recovering copper or nickel values from a wide variety of sources by various lixiviation (also interchangeably referred to as "leaching") processes. Unfortunately, not all sources behave the same in that some sources are much more readily leached than others. For example,.chalcocite is a copper mineral from which copper is readily recovered. Chalcopyrite, on the other hand, is much more difficult to leach but represents a potentially sizable source of copper. Copper and/or nickel can be involved in lixiviation either as the direct products of the process or indirectly as materials to be removed from a desired product. For example, chalcopyrite and other copper sources are leached from copper ores to recover copper, but can also be involved as contaminants such as those found in molybdenum concentrates which reduce the value of those concentrates. Removing some or all of the copper from a molybdenum concentrate significantly increases the value of the resulting concentrate. It would be desirable to have a process that could leach copper and/or nickel values even from a variety of copper and nickel sources. It would be particularly useful to have a process for recovering copper from sources, such as chalcopyrite, that have been considered difficult to leach. Only a handful of copper leaching processes have been commercialized over the years despite the number of processes suggested. Lixiviation with ferric chloride is a commonly practiced process. Unfortunately, the ferric chloride solution is highly corrosive to process equipment and is expensive to regenerate for reuse. Cyanide- containing solutions have also been attempted but with limited effectiveness. Several processes have been used with copper sulfide concentrates. The most widely publicized processes include the "Arbiter" process, the "Clear" process, and the "Cymet" process. The Arbiter process is described in The February 1974 issue of The Canadian Mining and Metallurgical Bulletin, pp. 62-73. Briefly described, the process contacts typical copper sulfide concentrate particles having a size of 70% -325 mesh (i.e., 70 wt% of less than 44 μm particle size diameter) with a lixiviation (leaching) solution containing ammonia and ammonium sulfate at 60° -90° C. Commercial oxygen is fed into the system at 5 psig. The lixiviation is performed in an apparatus that was essentially an enclosed flotation cell. In the Canadian Mining article, the authors suggest that the lixiviation of chalcopyrite is made more complicated than other minerals due to the formation of an iron oxide surface coating that blocks or inhibits oxygen contact with the ore surface for oxidation of the bound sulfides. As noted at page 65, "If, however, this iron oxide surface coating does not form or is not allowed to form, chalcopyrite can be leached as effectively as chalcocite, covellite, or bornite. " The solution proposed in the article was to employ "intense agitation" during the lixiviation process. The authors noted on page 67 that: "The relative horsepower draw of the impeller ... increased considerably in traversing the range of 400 to 1250 rpm. " Iron oxide that has precipitated in the bulk solution has a thickening effect (p. 65). The Clear process is described in Atwood et al. US Patent No. 3,785,944. In this process, chalcopyrite is oxidized with a lixiviation solution containing ferric chloride and cupric chloride to form a solution containing ferrous chloride and additional cupric chloride. Pyrite is taught as unaffected by the process (col. 4, line 4). The Cymet process is described in Clark et al. US Patent No. 4,341,742 in which chalcopyrite is leached with cupric chloride without ferric chloride or other additives. The stoichiometric proportions are carefully controlled to produce an extract high in cuprous chloride. As in the Arbiter process, the ore is sized to 95% -200 mesh (74 μm), preferably, 70% -325 mesh (44 μm). The lixiviation is conducted at a temperature above 80° C. Example 1 reports a 65% conversion of chalcopyrite to recoverable cuprous chloride. Other processes that have been suggested include Serciron US Patent No. 2,175,132 which describes the use of ammonia and a sulfur compound such as ammonium sulfite, bisulfite, hyposulfite or hydrosulfite with either air or oxygen to recover copper values from copper oxides or alloys (col. 2, lines 19-26). The examples describe batch extractions of non-sulfide copper sources. Example 2 reports a copper recovery of 32%. Probert et al. US Patent No. 3,911,076 describes a process for purifying molybdenum concentrates by contacting the concentrate with a solution containing ammonia and an ammonium salt (e.g., sulfate, carbonate, nitrate, chloride, or acetate). Oxides of cobalt, zinc, nickel, and copper are removed by the process. As taught, copper sulfides or native copper can be removed by contacting the solids in suspension with an oxygen-containing gas. The oxidized form is then removed in the leach solution. Kunda US Patent No. 3,985,553 describes a process for recovering copper from -100 mesh (less than 149 microns) copper sulfide particles by leaching them with ammonia and ammonium carbonate. The residue is separated and milled to scrub the external surface of the solids. The scrubbed residue is then re-leached in a second stage with fresh ammonia-ammonium carbonate solution. After the removal of free ammonia and carbon dioxide, the solution is oxidized and copper values are recovered by passing a reducing gas through the combined extracts to precipitate elemental copper. Ammonium sulfate free of sulfamatic contamination can also be produced under certain conditions. Kerley, Jr. US Patent No. 4,369,061 describes a lixiviation process for recovering silver and gold from manganese ores with a solution containing 2-60% ammonium thiosulfate, 0.05-0.1 % copper, and 0.05-4% sulfite. The copper can be supplied from the ore being treated or as a copper salt. The sulfite ions are used to inhibit the thiosulfate decomposition and prevent silver sulfide precipitation. Ammonium sulfite and bisulfite as well as "other sulfite salts" may be used to supply the sulfite ions. Horton et al. US Patent No. 4,880,607 describes a process for recovering uranium values from ores. The patent asserts that: "... numerous other valuable minerals, such as copper, nickel, molybdenum .... are also present in small quantities in subsurface formations, alone and quite often associated with uranium. Consequently, the recovery of such minerals is fraught with essentially the same problems as the recovery of uranium and, in general, the same techniques for recovering uranium can also be utilized to recover such other mineral values, whether associated with uranium or alone." While those in the copper recovery art may debate the general applicability asserted, Horton et al. describes oxidative leaching of uranium ore with either acidic or alkaline solutions in which the ore is separated into fines, i.e., a "slime" of -200 mesh (74 μm) generally and 91 % -400 mesh (37 μm) in the example, and coarse fractions (-14 X +200 mesh or 0.074-1.19 mm). An inert diluent of a size equivalent to the coarse fraction is added to the fines fraction and leached under mild conditions. The coarse fraction is leached under mild conditions based on the finding "that it is easier to leach uranium from the coarse fraction than the fines fraction. " (col. 5, lines 19-21) See also, Horton US Patent No. 4,892,715. Presently, there is no hydrometallurgical process in commercial operation specifically for the extraction of copper from copper sulfide concentrates. One commercial process primarily used for such recovery is smelting although leach recovery processes are going to become critical to the continued growth of copper recovery operations. Smelters that have traditionally been used to recover copper are operating at capacity with an increasing number of copper mines coming into production. If other recovery methods for purified copper are not found, additional smelting facilities will have to be built at great capital expense. It would be desirable to have a process for leaching copper values from chalcopyrite-containing ores, concentrates, and other sources of recoverable copper values with high recovery and economic process conditions. SUMMARY OF THE INVENTION It is an objective of the invention to provide a process for leaching copper values from chalcopyrite-containing ores, concentrates, and other sources of recoverable copper sulfides with high recovery and economic process conditions. It is an objective of the invention to provide a process for leaching nickel values from nickel-containing ores, concentrates, and other sources of recoverable nickel with high recovery and economic process conditions. In accordance with these and other objectives of the invention that will become apparent from the description herein, a process according to the invention comprises: extracting copper or nickel values from feed solids containing copper and/or nickel having at least 80 weight % thereof exhibiting an average particle size of less than about 75 microns by contacting said source under agitation and leaching conditions sufficient to recover copper and/or nickel from said feed by contact with: (a) a lixiviant comprising a mixture of ammonia and ammonium bisulfite, and (b) abrasive solid particles exhibiting at least 10 weight % of the solids exhibiting a particle size of greater than about 300 microns, under agitation and leaching conditions sufficient to suspend substantially all of said abrasive solid particles in scrubbing contact with said feed solids to continually expose new surfaces for contact with said lixiviant. The present invention provides a process for recovering copper and/or nickel values from copper and/or nickel-containing sources that exhibits a high recovery and process conditions that are readily performed on a commercial scale. DETAILED DESCRIPTION The invention relates to leaching of copper and/or nickel values from solid copper and/or nickel sources in the presence of relatively larger abrasive solid particles and a lixiviant containing ammonia and ammonium bisulfite. Solid copper sources that can be used as feed for the present process include copper or other metal concentrates, ores, slags, and flue dusts. Preferred copper sources for the present invention includes copper sulfide containing ores and concentrates such as those containing chalcopyrite in an amount within the range from about 0.01 wt% to about 100 wt%. As an example, molybdenite concentrates generally contain from about 1 wt% to about 5 wt% copper, a significant amount of which is in the form of chalcopyrite, which lowers the value of the concentrate. Solid nickel sources that can be used as feed for the present invention may be admixed with copper or copper-free. Exemplary minerals used as feed for the recovery of nickel according to the invention include pentlandite, garnierite, noumeite, millerite and other nickel sulfide materials, and niccolite. The solids used as feed to the present process preferably exhibit a fairly small particle size to present sufficient surface area for contact with the lixiviant. As is generally used in the copper extraction art, the copper-containing feed solids will be comminuted in a preliminary step to an average particle size of generally at least 50 wt% is less than about 74 μm (200 mesh), preferably at least 80 wt% is less than about 74 μm, and most preferably at least about 70 wt% is less than 44 microns (325 mesh). The abrasive solids useful in the present process are relatively larger and chemically distinct from the solid feed particles. In general, suitable abrasives exhibit an average particle size of greater than about 300 μm, preferably an average particle size within the range of about 300 μm to about 800 μm, and most preferably an average particle size within the range from about 400 μm to about 600 μm. The abrasive solids are preferably chemically inert towards the lixiviant as well as the leached species and should also exhibit a density, hardness, or other characteristic that permits separation thereof from the lixiviant. Suitable abrasives for the present invention include, inter alia, silica sand, quartz, magnetite, carborundum, and slag. The amount of abrasive solids used in the process is not subject to any critical minimum amount because the amount of solids necessary to scrub the surface of a particular feed will depend, among other things, on the agitation system in the leaching vessel, the particle size of the abrasive solids, and the particle size of the feed. In general, abrasive solids are used in a weight ratio of feed solids to abrasive solids within the range of 2:1 to about 9: 1. Preferably, the weight ratio of lixiviant to abrasive solids is within the range from about 2:1 to about 5:1. The lixiviant for the present invention is a mixture of ammonia (NH 3 ) and ammonium bisulfite (NH 4 HSO 3 ). The ammonium bisulfite can be added as a discrete component or formed in situ by passing sulfur dioxide thru the ammonia. This mixture, in the presence of dissolved copper and an oxidant (e.g., air or oxygen), dissolves copper and nickel from many feeds, even those with copper and nickel in otherwise leach resistant forms like chalcopyrite. The weight ratio of ammonia to ammonium bisulfite in the lixiviant is generally within the range from about 0.3 to about 0.8. This ratio does not change with the specific feed, but the total concentration of ammonia and ammonium bisulfite in the lixiviation solution is adjusted in proportion to the copper and nickel concentrations in the feed. The leaching process is preferably performed in a closed vessel at a pressure within the range from about ambient pressure to about 5 atmospheres. Preferably, the leaching process is performed at a pressure within the range from ambient to no more than about 3 atmospheres to avoid the need for costly pressure extraction vessels and the operating concerns associated therewith. A closed vessel eliminates loss of lixiviant during the process. The leaching process is generally performed at a temperature within the range from about 18° C (68° F) to less than about 300° C (572 °F). Preferably, the leaching process is performed at a temperature within the range from about 18° C to about 150° C (302° F). A combination of elevated heat and pressure could be used to increase the rate of copper dissolution and associated reactions if the capital and other expenses are economically warranted. The leaching process is performed with an agitation rate sufficient to suspend substantially, preferably 100%, of the abrasive solids in the lixiviant solution thereby causing the abrasive solids to scrub the surface of the feed solids and continually expose fresh mineral surface for leaching. Buildup of surface coatings on the feed solids that might inhibit leaching is effectively minimized thus resulting in faster kinetics and good overall extraction at a lower agitation rate. In general, leaching with agitated abrasives according to the present invention will extract copper and/or nickel values in a shorter extraction time than without the added abrasive solids and with a lower rate of agitation. Impeller rotation rates within about 450-1250 rpm were satisfactory for the leaching apparatus used in the following examples. Because the preferred agitation method in commercial operation is with an impeller suspended in the leach solution, the savings in time and power required for high rates of agitation provide for an economical, commercially viable process. EXAMPLES Examples 1 and 2 A molybdenite concentrate (56 wt% less than 53 μm) containing 4 wt% chalcopyrite was leached with a lixiviant containing ammonia and ammonium bisulfite (ABS) in the ammonia: ABS weight ratio of 0.6:1 at a pH of 10.4. Example 1 was performed without silica sand as the abrasive. Example 2 was performed with a 1:1 weight ratio of concentrate solids to silica sand abrasive (500 μm average particle size). An agitation rate sufficient to suspend all of the silica sand was used in both examples. The temperature and pressure were ambient for each of examples 1 and 2. In example 1, 63.8% of the copper was leached. In example 2, the use of sand abrasive increased the copper extraction to 75.3% under otherwise identical leaching conditions. Examples 3 and 4 A 27% copper concentrate according to the invention (68 wt% less than 53 μm) containing about 76% in the form of chalcopyrite was leached with the lixiviant of example 1. The process of example 3 was performed with silica sand (having an average particle size of about 500 μm). Example 4 was identical except that silica sand was not added. The agitation rate was the same for each example and was sufficient to suspend all of the silica sand used in example 3. The temperature and pressure were ambient. In example 3, 89.2% of the copper extraction was achieved in 2.5 hrs. Only 57.7% copper extraction was obtained after 3 hours in example 4. Examples 5-7 Examples 5-7 compare the effectiveness of lixiviant solutions when the temperature and pressure are at ambient conditions. Silica sand abrasive having the size of examples 2 and 3 were used in each example with all examples subjected to the same agitation rate during the leaching. In example 5, a copper concentrate was leached for 2 hours with a lixiviant contaimng an ammoma: ABS ratio of 0.8: 1. In 2 hours, the extraction was 49.2%. Extending the extraction time to 7 hours increased the extraction to 93 % . In example 6, a sample of the same concentrate used in example 5 was leached with a lixiviant made from ammonia and ammonium sulfate (AS) in a ratio of ammonia: AS of 0.8: 1. The sample was leached for 4 hours and extracted 43.1 % of the copper. In example 7, the same concentrate was leached with only aqueous ammonia for 3 hours, only 41.6% of the copper was extracted. Example 8 Molybdenum concentrate, sized according to the invention and having 3.3% copper, was leached for seven hours with the lixiviant of example 1 in an agitated, closed leaching vessel containing silica sand particles of about 500 μm diameter. Of the copper in the concentrate, 96.4% was removed leaving a molybdenum concentrate with 0.14 wt% copper. The following Table 1 summarizes the results of examples 1-8. Table 1 Copper Example Feed Lixiviant Abrasive Time (for.) Extraction (%) 1 Mo concentrate ammonia/ABS none 4 63.8 2 - ammonia/ABS silica 4 75.3 3 Cu concentrate ammonia/ABS silica 2.5 89.2 4 ammonia/ABS none 3 57.7 5 " ammonia/ABS silica 2 49.2 7 93 6 ammonia/ silica 4 43.1 ammonium sulfate 7 • ammonia silica 3 41.6 8 Mo concentrate ammonia/ABS silica 7 96.4 Examples 9-10 Examples 9 and 10 were extractions of the copper concentrate used in examples 3-7 using the ammonia/ABS lixiviant of example 1 both with (ex. 9) and without (ex. 10) abrasive silica sand having an average particle size of 500 μm. The agitation rate for each example was the same. The copper extraction between each hour was determined by conventional assay on a small sample of the feed solids. The results are reported in Table 2. Table 2 Copper Extraction (%) Example Hour 1 Hour 2 Hour 3 Hour 4 Hour 5 Total 9 34 24 17.1 1 1.7 6.9 93.7 10 31 10.5 * 12.6 * 6.2 _ 60.3 The assay results from these samples appear to be reversed from the expected copper extraction rates. A comparison of the results in Table 2 shows that the extraction rates in both examples slows as the amount of available copper is reduced in the feed. With the addition of silica sand particles to the process, however, the extraction is significantly more effective over the duration of the process. The net result is an overall higher extraction of copper from the feed. If the examples were terminated at roughly the same overall extraction (about 60%), the process of the invention (ex. 9) would provide in just over 2 hours what required 4 hours from the abrasive-free process (ex. 10). It will be understood that the foregoing examples are presented to illustrate the invention and are not intended to act as a limitation on the scope of the appended claims.

Claims: CLAIMS 1. A process for leaching copper and/or nickel-containing solids, said process comprising: extracting copper and/or nickel values from copper-containing feed solids having at least 50 weight % of said solids exhibiting an average particle size of less than about 75 μm by contacting said feed solids with: (a) a lixiviant comprising a mixture of ammonia and ammonium bisulfite, and (b) abrasive solid particles exhibiting an average particle size of greater than about 300 μm, wherein the extracting step comprises agitation conditions sufficient to suspend substantially all of said abrasive solid particles in scrubbing contact with said feed solids to continually expose new surfaces for contact with said lixiviant. 2. A process as in claim 1 wherein the contacting step comprises: contacting said feed solids with abrasive solid particles in a weight ratio of feed solids to abrasive solid particles within the range from about 2:1 to about 9: 1. 3. A process as in claim 1 wherein the contacting step comprises: contacting said feed solids with abrasive solid particles in a weight ratio of feed solids to abrasive solid particles within the range from about 2:1 to about 5:1. 4. A process as in claim 1 wherein the contacting step comprises: contacting said feed solids with said lixiviant and abrasive solid particles exhibiting an average particle size within the range from about 300 μm to about 800 μm. 5. A process as in claim 1 wherein the contacting step comprises: contacting said feed solids with said lixiviant and abrasive solid particles exhibiting an average particle size within the range from about 400 μm to about 600 μm. 6. A process as in claim 1 wherein the contacting step comprises: contacting said feed solids with said lixiviant and abrasive solid particles selected from the group consisting of silica sand, quartz, magnetite, and carborundum. 7. A process as in claim 1 wherein the contacting step comprises: contacting said feed solids with said lixiviant and silica sand. 8. A process for leaching copper-containing solids, said process comprising: extracting copper values from copper-containing feed solids having at least 50 weight % of said solids exhibiting an average particle size of less than about 75 μm by contacting said feed solids with: (a) a lixiviant comprising a mixture of ammonia and ammonium bisulfite, and (b) abrasive solid particles exhibiting a particle size of at least 10 weight % thereof greater than about 300 μm wherein the extracting step comprises agitation conditions sufficient to suspend substantially all of said abrasive solid particles in scrubbing contact with said feed solids to continually expose new surfaces for contact with said lixiviant. 9. A process as in claim 8 wherein the contacting step comprises: contacting said feed solids with abrasive solid particles in a weight ratio of feed solids to abrasive solid particles within the range from about 2:1 to about 9: 1. 10. A process as in claim 8 wherein the contacting step comprises: contacting copper-containing feed solids containing copper sulfides with said lixiviant and said abrasive solid particles. 11. A process as in claim 8 wherein the contacting step comprises: contacting copper-containing feed solids comprising molybdenite concentrate with said lixiviant and said abrasive solid particles. 12. A process as in claim 8 wherein the contacting step comprises: contacting said feed solids with said lixiviant and abrasive solid particles exhibiting an average particle size within the range from about 300 μm to about 800 μm. 13. A process as in claim 8 wherein the contacting step comprises: contacting said feed solids with said lixiviant and abrasive solid particles exhibiting an average particle size within the range from about 400 μm to about 600 μm. 14. A process as in claim 8 wherein the contacting step comprises: contacting said feed solids with said lixiviant and abrasive solid particles selected from the group consisting of silica sand, quartz, magnetite, and carborundum. 15. A process as in claim 8 wherein the contacting step comprises: contacting said feed solids with said lixiviant and silica sand. 16. A process for leaching nickel-containing solids, said process comprising: extracting nickel values from nickel-containing feed solids having at least 50 weight % of said solids exhibiting an average particle size of less than about 75 μm by contacting said feed solids with: (a) a lixiviant comprising a mixture of ammonia and ammonium bisulfite, and (b) abrasive solid particles exhibiting a particle size of at least 10 weight % thereof greater than about 300 μm, wherein the extracting step comprises agitation conditions sufficient to suspend substantially all of said abrasive solid particles in scrubbing contact with said feed solids to continually expose new surfaces for contact with said lixiviant.

Inventors: BUZA THOMAS B, KLING HEINRICH, NEYLON RICK JAMES, WILSON JOSEPH P, BUZA, THOMAS, B., KLING, HEINRICH, NEYLON, RICK, JAMES, WILSON, JOSEPH, P.
Applicants: BUZA THOMAS B, HICKSON KERLEY INC, KLING HEINRICH, NEYLON RICK J, WILSON JOSEPH P, BUZA, THOMAS, B., HICKSON KERLEY, INC., KLING, HEINRICH, NEYLON, RICK, JAMES, WILSON, JOSEPH, P.
Application year: 1994
Main classification: B01F1
IPC codes: B01F1, C22B15